Method of assembling electrochemical cells of novel construction

ABSTRACT

A lithium halide button cell formed of simplified sub-assemblies including one such subassembly in which molten cathode material is poured into a retaining ring and allowed to solidify therein before incorporation into the cell.

This is a divisional of application Ser. No. 08/054,778 filed on Apr.27, 1993, now pending.

BACKGROUND OF THE INVENTION FIELD OF THE INVENTION

This invention relates to the fabrication of electrochemical cellsgenerally. Specifically, it is concerned with a method of fabricatingelectrochemical cells from sub-assemblies of novel construction and withthe novel structure of the resultant electrical chemical cellsthemselves. In a preferred embodiment, the active anode and cathodematerials of such cells are lithium anode materials and halogen cathodematerials such as iodine or a polyiodide contained in an organiccomponent material such as polyvinylpyridine or poly-2-vinylpyridine maybe included between the anode proper and the cathode proper.

In the past, such cells making use of such halogen cathode materialshave been assembled within a container. The molten cathode material waspoured through an opening in the cell container after its mainstructural components had been assembled within the cell container.Thereafter, the fill opening was sealed. For purposes of this inventionthe term "fluid" is meant to describe any cathode component materialcapable of flowing during at least some step of cell fabrication. Thefollowing listed U.S. patents show various lithium-halogen batteries orelectrochemical cells making use of cell containers into which a fluidcathode component is introduced into the container through a filleropening: 4,105,833; 4,135,519; 4,132,836; 4,166,887 and 4,211,832. Otherpatents of interest are U.S. Pat. Nos. 4,217,403 and 3,874,929.

Other electrochemical cells incorporating different components may makeuse of this invention. It should be understood for purposes of thisinvention that the fluid component used needs to be in fluid form onlyat the time of cell fabrication or assembly. Thereafter it may solidifyfor cell operation.

SUMMARY OF THE INVENTION

This invention provides an improvement in electrochemical cellfabrication wherein the cathode component is introduced into asubassembly rather than into the assembled electrochemical cellstructure through a fill port. As a result, novel assembly methods andnovel cell constructions are provided which are simpler and easier toassemble and therefore lead to low cost manufacture.

BRIEF DESCRIPTION OF THE DRAWINGS

A detailed description of the invention is hereafter described withspecific reference being made to the drawings in which:

FIG. 1 is a perspective view of an electrochemical cell illustrating thenovel construction of the invention.

FIG. 2 is a side elevational view in section along line 2--2 of FIG. 1.

FIG. 3A through FIG. 3E are simplified sectional diagrams of ananode/cathode subassembly during fabrication in a holding die.

FIG. 3F is a top plan view of a preferred cathode current collector leadstructure used in the subassembly of FIGS. 3A through 3E.

FIG. 4 is a sectional exploded view showing of the varioussub-assemblies of a preferred electrochemical cell according to theinvention demonstrating how they fit together for final assembly.

FIG. 5 is a sectional assembly view of an electrochemical cell similarto that of FIG. 2 showing an optional retaining ring construction.

DETAILED DESCRIPTION OF THE INVENTION

Referring now specifically to FIGS. 1 and 2, a sealed lithium-halogencell is illustrated showing a preferred application of the invention.The cell comprises a bottom enclosure portion 10 which may take the formof a shallow metal can or container of any predetermined configurationsuch as a round container for preparing a "button" cell of the typeillustrated. Container 10 may be stainless steel the open top of whichis closed by means of a substantially flat top portion or cover 12, alsoof stainless steel. Top and bottom portions 10 and 12 respectively, arewelded together as a last assembly step to provide a sealed container.The cell further includes anode means comprising a lithium element 14having an anode current collector element 18. Current collector 18 is arelatively thin metal element, which may be formed with apertures (notshown) for establishing intimate contact with the relatively softlithium anode. Collector 18 may be formed of a variety of metals such asnickel, zirconium, stainless steel, etc. A conductor lead feedthroughassembly generally indicated at 20 includes a pin 22 of stainless steelor other suitable metal which is butt welded to collector 18 and is ofsufficient length to extend out of the feedthrough structure 20 formaking an external electrical connection thereto. Pin 22 is sealed fromthe remainder of the cell by means of the feedthrough structure 20 whichincludes a glass insulator element 24 and an upstanding metal ferruleelement 26. Ferrule 26 may be a separate element welded to top 12 or itmay be an integral upset element formed from top 12 by metal stamping orthe like. Underneath lithium anode 14 is the halogen cathode material28. The cell is shown as including with the anode a polymer film 30 suchas polyvinylpyridine, poly-2-vinylpyridine or the like. The polymer filmis preferred but not necessary. Hence, it may be omitted. The anode,cathode and polymer film are surrounded by a retaining ring 32 comprisedof a flat inert plastic band having upper and lower edges as shown inthe Figure. Any non-reactive plastic is suitable for retaining ring 32which is inert to the cell contents and which can serve as a frameretaining member for the active anode and cathode components. Typically,a modified polytetrafluoroethylene such as Tefzel™ a copolymer ofethylene and tetrofluoroethylene manufactured under this trademark by E.I. DuPont De Nemours Company of Wilmington, Del. 19898, is preferred.However, a fluoropolymer such as Halar™ a trademark of Allied ChemicalCompany or a polyvinylidenefluoride sold under the trademark Kynar™ byPenwalt Corporation of Philadelphia, Pa. 19102, is also acceptable.Other materials will be useable by those familiar with this art.

The anode/polymer film/cathode/retaining ring subassembly is shown inFIG. 2 as being received into an inverted cup-shaped insulator 34, alsoof non-reactive plastic of any of the aforementioned types or evenpolypropylene. Another subassembly is provided by the top portion 12,pin 22, insulator cup 34 and anode collector 18. These twosub-assemblies will be discussed further hereinbelow. For the present itis sufficient to note that the anode subassembly is positioned withinthe insulator cup subassembly with the anode 14 lithium surface inintimate contact with the anode current collector 18 and the bottom ofthe insulator cup 34 as shown in FIG. 2.

As already indicated, the halogen cathode material 28 may be any of thevarious materials known in the art such as iodine or a polyiodidecontained in an organic component material such as polyvinylpyridine orpoly-2-vinylpyridine or the like. This type of cathode material is wellknown and incorporated into the cell in the form of a fluid or moltenmaterial which is allowed to solidify upon cooling.

Referring now to FIGS. 3A-3F the fabrication procedure as modified bythe present invention for fabricating a subassembly of simplifiedstructure and simplified fabrication procedure will now be described.The fabrication of the anode/polymer film/cathode subassembly is begunby providing a fixture or die 40 which will preferably be of acylindrical shape as shown in FIGS. 3A-3E and may be of any relativelyheavy tool metal as is typically used in the art for die purposes. Die40 may have an open top and bottom end as shown or the bottom may beenclosed as an option. In either event, a parting sheet of suitableplastic 42 is placed at the bottom of the die to receive retaining ring32 as shown in FIG. 3A. Next, as shown in FIG. 3B, a slightly undersizeddisc of lithium metal is placed into the retaining ring and may bepressed until the lithium flows to fill the internal diameter ofretaining ring 32. A disc of separator film 30 such aspoly-2-vinylpyridine is next placed into ring 32 over the top of thelithium anode as shown in FIG. 3C. The film may be pressure bonded tolithium during pressing. Then, the molten cathode material is pouredinto the ring over the separator film 30 as shown in FIG. 3D. The ringmay be filled to its upper edge with the cathode material or a slightspace may be left as shown in FIG. 3D to leave room for an optionalmetal cathode current collector of the type shown in FIG. 3F. Currentcollector 42 as shown in 3F includes a round body portion 42a and a leadportion 42b and may be positioned over the cathode material 28 as shownin FIG. 3E. Cathode current collector 42 will typically be of stainlesssteel and will be extremely thin almost of a foil thickness. Intimatecontact between the cathode and cell container with or without thecollector allows the container to function as the cathode connection forthe cell.

Referring now to FIG. 4, the top/insulator cup/anode collectorsubassembly is best seen and understood in terms of its assembly. Cover12 fitted with feedthrough 20 is mated with pin 22 which has been buttwelded to collector 18 after the inverted insulator cup 34 has beenfitted over the pin and collector 18 has been brought into contact withthe relatively large surface area of pin 22 for welding. Attachment byslip fit, crimping, etc., may be used in place of welding. At thispoint, this subassembly is ready to be mated with theanode/cathode/separator subassembly as shown in the Figure with thelithium surface positioned for contact with collector 18. Retaining ring32 is shown in this Figure with an optional structural variationincluding an inwardly directed flange on its upper end at 32a as shownin the Figure. This subassembly is merely received in insulator cup 34followed by placement of can 10 the flange 10a of which is then weldedto cover 12 to seal the cell. The cathode collector 42 may be includedif desired but is not shown in this Figure.

It will be readily seen that by providing step-wise assembly by way ofsub-assemblies any necessity to scrap any portion of a subassembly willhave minimal cost effects because the entire cell is not involved at anyof these subassembly stages. Moreover, such sub-assemblies lendthemselves to simplified fabrication procedures such as handling and thelike leading to lower cost. The subassemblies may, of course, be puttogether in reverse order to that described herein.

As has already been pointed out in connection with FIG. 4, an optionalconfiguration of retaining ring 32 may include an inwardly extendingflange 32a which may be used as desired. Another variation is shown inFIG. 5 which includes an outwardly extending flange 32b. This flangearrangement is most preferred as it can be utilized to position aretaining ring 32 of lesser diameter as may be desired in those caseswhere adjustment of the cell capacity is needed.

While the preferred embodiments have been described in detail, this hasnot been done for purposes of limitation but by way of illustration. Theinvention is intended to be defined by the following claims.

This completes the description of the preferred and alternateembodiments of the invention. Those skilled in the art may recognizeother equivalents to the specific embodiment described herein whichequivalents are intended to be encompassed by the claims attachedhereto.

What is claimed is:
 1. A button cell comprised of preassembled activecomponents within a retaining ring, the cell comprising;top and bottommetal enclosure portions, the top portion including a sealed pinfeedthrough structure extending through the top portion to an interiorsurface thereof, an inverted plastic insulator cup positioned againstthe interior surface thereof with the pin extending therethrough, and acollector disk attached to an interior end of the pin, the disk beingpositioned against a bottom of the inverted insulator cup; a retainingring subassembly including a flange on one edge, enclosing the ring,lithium anode layer positioned on the flanged edge, a P2VP film againstan interior surface of the anode layer within the ring and a solidifiedlayer of cathode I₂ /P2VP against the film, the ring subassembly beingpositioned with the anode surface and ring flange against the bottom ofthe insulator cup whereby the anode contacts the collector and theflange on the ring positions the subassembly in the insulator cup, andthe bottom enclosure portion is positioned against the cathode surfaceand secured to the top portion to form a sealed enclosure.
 2. The buttoncell of claim 1 including a cathode collector between the cathode andthe bottom enclosure portion.
 3. The button cell of claim 1 wherein theflange extends around the outer periphery of a retaining ring edge. 4.The button cell of claim 1 wherein the flange extends around an innerperiphery of the retaining ring edge.
 5. The button cell of claim 1wherein the flange extends around an inner and outer periphery of theretaining ring edge.
 6. The button cell of claim 1 wherein a diameter ofthe ring is selected to provide a predetermined retaining ring size andamount of anode and cathode materials therein for capacity control.